The advent of information society is closely related to a steady increase in the usage of mobile communication devices. Such mobile communication devices technically evolved from, and still include, mobile telecommunication devices. A typical setup thus includes a telecommunication network comprising a plurality of spatially distributed base stations and a varying number of mobile communication devices connected to one or more of the base stations.
For reliable exchange of data in the telecommunication network, telecommunication standards such as Universal Mobile Telecommunications System (UMTS) or Long Term Evolution (LTE), which are defined by the 3rd Generation Partnership Project (3GPP), use Hybrid Automatic Repeat Request (HARQ) transmissions. HARQ transmissions allow the mobile communication device to selectively request retransmissions of individual information packets based on a timely feedback from the mobile communication device to the base station depending on whether the information packets have been successfully received or not.
In LTE, the information packets are segmented into individually decodable blocks, each of which includes an individual Cyclic Redundancy Check (CRC) value. The mobile communication device feedbacks a Negative Acknowledge (NAK or NACK) signal to the base station in the case of a reception error. The base station has no knowledge of the CRC status of each of the individual blocks as received by the mobile communication device. Thus, the base station transmits all blocks again in response to a HARQ retransmission request. The bandwidth associated with the retransmission of already successfully received blocks is wasted.
In current telecommunication standards, including UMTS and LTE, spatial multiplexing is used to increase spectral efficiency, i.e., to increase the number of transferable bits per time and frequency, by transmitting more than one block at the same time using more than one transmit antenna and more than one receive antenna. Usage of such a Multiple Input Multiple Output (MIMO) channel for the transmission significantly increases a decoding complexity at the receiving side. Limited computational resources of the mobile communication device often only allow approximating an optimal symbol detector by a sub-optimal variant, such as Sphere Decoding.